In typical bicycle gear shift devices, a shift control cable transmits the force of an actuating member operable by a bicyclist, to a derailleur arranged adjacent to the sprockets. To protect the cable from damage caused by environmental conditions, such as dirt or moisture, a sleeve is generally provided on the shift control cable. However, even when utilizing a sleeve, portions of the shift control cable, such as the portion of the cable between the end of the cable sleeve and the derailleur, remain exposed and are thus susceptible to damage. This is particularly disadvantageous for the portions of the shift control cable that are close enough to the road surface such that dirt and mud from the road surface can precipitate on the cable. Continued exposure to the road condition causes dirt to accumulate on the shift control cable, which eventually impedes the motion of the cable in and out of the cable sleeve. As a result, the shifting mechanism may then be movable either by great force only or not at all.
Another disadvantage of the cable operated gear shift systems is that the shift control cable tends to stretch over a period of time and thus the derailleur mechanism needs to be adjusted in order to effect proper shifting of gears. Additionally, the cable frequently becomes rusted or worn and accordingly will break when a gear change is attempted. Installation and maintenance of the control shift cable is complicated and requires the elimination of any kinks and bends in the cable that can result in additional frictional force between the cable and the sleeve.
To overcome the disadvantages of cable operated gear shift systems, hydraulically operated systems have been proposed. However, the problem with the known hydraulic gear shift systems is that the mechanisms used for indexed shifting are less sophisticated and imprecise. Accordingly, it is desirable to provide a hydraulic gear shift mechanism having a control device that provides precise positioning for indexed shifting.
Another disadvantage of known hydraulically operated gear shift systems is that if the system needs an adjustment, an end point adjustment is typically made at the slave cylinder assembly to adjust the initial position of the slave piston. Given that the slave cylinder assembly is located near the derailleur, it is inconvenient to a bicycle rider to make an adjustment at that location. Accordingly, it is desirable to provide an adjuster at a location that is easily accessible to the rider.